Is my WFCO converter/charger killing my batteries?

You may have a defective converter. If you can run your generator, a separate charger sounds like a better idea in the short term.

There is usually a fairly wide range of allowable charging voltages, so I wouldn't fret over the difference between 14.6 and 14.8V.

As to equalization, "Trojan only recommends equalizing when low or wide ranging specific gravity (>0.030) are detected after fully charging a battery."

OK so you have one of the bigger 2 way only fridges. In that case just leave the loads you have on for longer before starting the charger. The furnace fan is another load you can add but you'll use up some propane doing that.

I had a WFCO fail the opposite way, charged at 15.5V and never went lower. While there are those on this forum who think we'll if WFCO in my opinion they are not the best.

So if you can't get it to go into absorption mode then I agree, consider getting a new charger. Don't expect it to go into or stay in bulk charge mode for long though.

Folks seem to like Progressive Dynamics and I think they make one that will fit in the current WFCO location. You can look at going to a 55A charger but check your wire ampacities and fuses. Otherwise a second charger connected directly to the batteries might be an easier way to increase charge rate/generator loading. It won't hurt anything running two chargers although you might have trouble pushing as much current into your batteries as you seem to want to (because the chargers will autonatically step down to loser charge rates). Having ajustable output voltage/current would help, so also consider a DC power supply where you have direct control of the output current and voltage limits.

I've been designing lead acid battery systems for 40+ years and I've never heard of a manufacturer saying it's ok to draw a lead acid battery all the way down. So either thats one really really old theory of operation or that customer service person is blowing smoke as cover for a (shall we say?) less than optimized charger design.

If youre getting around 13.6 that looks like absorption mode is working but as many others report you aren't getting into bulk mode charging, and it's interesting that WFCO is acknowledging that.

The test with the battery disconnected is good information, faster than waiting for a low enough SOC. I wonder if you could do the same test with more load and get bulk mode to kick in?

So while I think most folks find the WFCO to charge their GC deep cycle or other batteries OK I don't think you will ever be satisfied. You are clearly a knowledgeable and attentive user which most folks are not. I suggest you get a charger or power supply with adjustable output voltage (and perefably current) which will give you full control over what it's doing.

One other thing, some chargers/power supplies have battery voltage sense lines separate from the current carrying conductors. Using those as the voltage reference eliminates the effect of resistive voltage drop in the the main current carrying conductors so the charger can be placed remotely from the battery without picking up a voltage measurement error. this capability is commonly available in solar charge controllers and in power supplies, not sure how common it is in chargers.